Answer
A person who acts within a justifying circumstance under Article 11 of the Revised Penal Code — such as self-defense, defense of a relative, or defense of a stranger — does not incur criminal liability, because the law considers the act lawful rather than merely excused. It follows that, as a rule, there is also no civil liability arising from the act, since no crime is deemed to have been committed.
The recognized exception is the state of necessity in paragraph 4 of Article 11 (causing damage to avoid a greater evil or injury). Under Article 101, in that situation there is no criminal liability, but civil liability attaches to the persons who benefited from the act, in proportion to the benefit they received. The distinction matters: justification removes the crime, but the law still allocates the loss where someone was spared a greater harm.